The present invention relates to a signal input sheet to output a signal indicative of the position of a pressure applied onto the sheet surface in accordance with the pressure.
Such a signal input sheet has been well known by, for instance, JP-A-60-51928 and JP-A-61-43332. FIG. 2 is a cross sectional view of a fundamental construction of such a signal input sheet. A signal input sheet 10 comprises a lower laminate 10A and an upper laminate 10B having a flexibility. The lower laminate 10A has a structure in which a rigid base plate 11 made of aluminum or the like, an insulative board 12 made of a phenol resin, a glass epoxy resin, or the like, and a resistance layer 14 having a predetermined resistance ratio are laminated. On the other hand, the upper laminate 10B has a structure in which a conductive layer 16, a rubber-like elastic layer 18 having a flexibility, a shielding layer 20 to eliminate static electricity from the hand of a user or noises from the outside, a printed layer 22 on which a print for a predetermined display was executed, and a transparent protective layer 24 are laminated in the direction from the lower side to the upper side. The elastic layer 18 is made of, for instance, elastomer. The conductive layer 16 is formed by thinly coating a conductive ink onto the elastic layer 18.
Dot-shaped insulative spacers 26 are adhered onto the lower surface of the upper laminate 10B so as to allow the conductive layer 18 to be away from the resistance layer 14 by a predetermined distance, thereby always keeping the conductive layer 16 and the resistance layer 14 in an electrically contactless state. A number of insulative spacers 26 are arranged on the lower surface of the conductive layer 16 in a form like a mesh or dots as shown in FIG. 3. The insulative spacers 26 have an elasticity such that they are easily deformed and recovered by a predetermined pressure or more, namely, by an ordinary hand-writing pressure.
When a pressure is applied from the surface of the transparent protective layer 24 to the upper laminate 10B by using a pen or the like, the upper laminate 10B becomes depressed in the pressurized portion. Thus, several insulative spacers 26 existing at a location corresponding to the pressurized position are also deformed and the conductive layer 16 is come into electrical contact with the resistance layer 14. Therefore, when a predetermined voltage V.sub.cc has previously been applied between the conductive layer 16 and the resistance layer 14, a current at the time of the electrical connection of the conductive layer 16 and the resistance layer 14, that is, a resistance value of the portion of the resistance layer 14 can be known from the voltage drop of a resistor R. Since such a resistance value corresponds to the pressurized position, X-Y coordinate signals of the pressurized position can be obtained. The upper laminate 10B is obviously recovered to the original state by releasing the hand-writing pressure.
By using the signal input sheet of the above conventional example to a signal input apparatus, hand-written information, for instance, hand-written characters of figures can be inputted. The signal input sheet is a flat plate and can be cheaply manufactured. On the other hand, as compared with an ordinary keyboard device using mechanical switches, the stable operating characteristics which are difficult to be influenced by the external environment are obtained. Therefore, it is expected that such a signal input sheet is applied to a simple data input terminal.
In the above two conventional techniques, the insulative spacers are arranged at regular intervals and the whole input sheet can respond at an equal sensitivity for an input pressure applied from the outside.
In such an input sheet, in addition to the input means by the hand-writing pressure, alphabet keys or KATAKANA character keys, a ten-key, other various command keys, and work content keys are also provided. Since those keys are based on the input of what is called binary data of ON/OFF, the sensitive conditions by the input largely differ from those by the input due to the hand-writing pressure.